Field of the Invention
The present invention relates to a solid-state imaging device and an imaging apparatus which include a plurality of pixels and in which a first substrate and a second substrate having circuit elements of the pixels arranged thereon are electrically connected to each other by a connecting portion.
Description of Related Art
In recent years, video cameras, electronic still cameras, and the like have become generally widespread. Such cameras employ a charge-coupled device (CCD) type solid-state imaging device or an amplification type solid-state imaging device. The amplification type solid-state imaging device introduces signal charges, which are generated and stored by photoelectric conversion elements of pixels on which light is incident, into amplification elements of the pixels and outputs signals, which are amplified by the amplification elements, from the pixels. In the amplification type solid-state imaging device, such pixels are arranged in a two-dimensional matrix shape. Examples of the amplification type solid-state imaging device include a complementary metal oxide semiconductor (CMOS) type solid-state imaging device using CMOS transistors.
In the related art, a general CMOS type solid-state imaging device employs a method of sequentially reading out signal charges, which are generated by photoelectric conversion elements of pixels arranged in a two-dimensional matrix shape, for each row. In this method, since exposure timings in the photoelectric conversion elements of the pixels are determined depending on a start and an end of reading-out of the signal charges, the exposure timings differ depending on the rows. Accordingly, when a fast-moving subject is imaged using the CMOS type solid-state imaging device, a distortion of the subject occurs in the captured image.
In order to remove the distortion of a subject, a simultaneous imaging function (a global shutter function) of realizing simultaneous storage of signal charges has been proposed. The number of applications of the CMOS type solid-state imaging device having a global shutter function is increasing. The CMOS type solid-state imaging device having a global shutter function generally needs to include shaded memory elements in order to store signal charges generated by the photoelectric conversion elements until the signal charges are read out. In such a CMOS type solid-state imaging device, after all pixels are simultaneously exposed, signal charges generated by the photoelectric conversion elements are simultaneously transferred to the memory elements in all the pixels and are temporarily stored therein, and the signal charges are sequentially converted into pixel signals and read out at a predetermined readout timing.
However, in the CMOS type solid-state imaging device having the global shutter function in the related art, the photoelectric conversion elements and the memory elements have to be formed on the same plane of the same substrate, and thus an increase in chip area is inevitable. In a waiting period until the signal charges stored in the memory elements are read out, signal quality degrades due to noise based on light or noise based on a leakage current (dark current) generated in the memory elements.
In order to solve this problem, a method is disclosed of preventing an increase in chip area and reducing noise using a solid-state imaging device in which a first substrate having photoelectric conversion elements formed thereon and a second substrate having memory elements storing signal charges (electrical signals) generated by the photoelectric conversion elements formed thereon are bonded to each other (for example, see Japanese Unexamined Patent Application, First Publication No. 2012-79861).
FIG. 8 illustrates an example of a process of manufacturing a solid-state imaging device in which two substrates are bonded to each other. In FIG. 8, cross-sections of the two substrates are schematically illustrated. Steps illustrated in FIG. 8 will be described below.
First, a first substrate 90 and a second substrate 91 are prepared and bonded to each other. The first substrate 90 includes a first semiconductor layer 910 having photoelectric conversion elements 911 formed therein and a first interlayer film 920 having a first wiring layer 921 formed therein. The second substrate 91 includes a second semiconductor layer 930 having memory elements (not illustrated), which store electrical signals generated by the photoelectric conversion elements 911, formed therein and a second interlayer film 940 having a second wiring layer 941 formed therein. The first substrate 90 and the second substrate 91 are bonded to each other in a state in which the first interlayer film 920 and the second interlayer film 940 face each other. In the state in which the first substrate 90 and the second substrate 91 are bonded to each other, the first wiring layer 921 and the second wiring layer 941 are connected to each other by a connecting portion 950.
In the first semiconductor layer 910 of the first substrate 90, the photoelectric conversion elements 911 are formed on a front surface side (a side on which the first interlayer film 920 is formed) of the first semiconductor layer 910. The opposite surface (a surface exposed to the outside) of the surface in contact with the first interlayer film 920 is the rear surface of the first semiconductor layer 910.
After the bonding is performed, the rear surface of the first semiconductor layer 910 is ground such that light is incident on the photoelectric conversion elements 911. Since the first interlayer film 920 is very thin, generally, the grinding of the rear surface of the first semiconductor layer 910 is performed after two substrates are bonded to each other. After the grinding, a large amount of light incident from the rear surface of the first semiconductor layer 910 is absorbed by the first semiconductor layer 910 and thus disappears. However, since the first semiconductor layer 910 is thin, some light is transmitted by the first semiconductor layer 910 and is incident on the first interlayer film 920. When the light transmitted by the first semiconductor layer 910 is incident on the memory elements formed in the second semiconductor layer 930 of the second substrate 91, noise is mixed into signals. In order to prevent this mixture of noise, the first wiring layer 921 and the second wiring layer 941 are arranged to block the light transmitted by the first semiconductor layer 910.
Before the first substrate 90 and the second substrate 91 are bonded to each other, an operation check and a characteristic check are performed on the individual substrates. The operation check is to check whether the solid-state imaging device operates in accordance with a control signal when the control signal is supplied from the outside. The characteristic check is to check whether signals generated from the solid-state imaging device have linearity with respect to an amount of light incident thereon. The operation check and the characteristic check of the first substrate 90 and the second substrate 91 are performed in a state in which light is incident on the photoelectric conversion elements 911.